Double spin filter tunnel junction

ABSTRACT

A memory device that includes a first magnetic insulating tunnel barrier reference layer present on a first non-magnetic metal electrode, and a free magnetic metal layer present on the first magnetic insulating tunnel barrier reference layer. A second magnetic insulating tunnel barrier reference layer may be present on the free magnetic metal layer, and a second non-magnetic metal electrode may be present on the second magnetic insulating tunnel barrier. The first and second magnetic insulating tunnel barrier reference layers are arranged so that their magnetizations are aligned to be anti-parallel.

BACKGROUND

Technical Field

The present invention relates to magnetic random access memory devicesand apparatuses, and more particularly to spin transfer torque cells formagnetic random access memory.

Description of the Related Art

Magnetic random access memory (MRAM) devices differ from conventionalrandom access memory (RAM) in that data is stored through the use ofmagnetic elements as opposed to storing data through electric charges orcurrent flows. In accordance with MRAM, two magnetic elements areseparated by a barrier. In addition, one of the magnetic elements can bea permanent magnet set to a fixed polarity while the polarity of theother magnetic element is adaptable to store data. The different digitalstates (i.e. one or zero) can be differentiated by assessing whether thepolarity of the two elements are the same or different. Data can be readby measuring the electrical resistance of the cell. For example, atransistor can switch a current through the cell such that chargecarriers tunnel through the barrier in accordance with the tunnelmagneto resistance effect. The resistance of the cell is dependent onthe magnetic moments of the two elements. Writing data in an MRAM can beconducted using a variety of methods. Spin transfer torque (STT), whichemploys a spin polarized current, is one such method.

In accordance with STT, the spin-polarized current is altered as itpasses through the adaptable magnetic element, thereby applying a torqueto the magnetic element and changing its polarity. Further, there aremultiple types of STT MRAM devices. For example, reference layers andfree layers of in-plane STT MRAMs have magnetic moments that areparallel to the wafer plane. Alternatively, reference layers and freelayers of Perpendicular Magnetic Anisotropy (PMA) STT MRAMs havemagnetic moments that are perpendicular to the wafer plane.

SUMMARY

In one embodiment, a spin torque transfer magnetic random access memorydevice is provided in which the tunnel barriers and pinned layers of aconventional device have been replaced with magnetic insulating tunnelbarrier reference layers. In some embodiments, the memory deviceincludes a first non-magnetic metal electrode, and a first magneticinsulating tunnel barrier reference layer present on the firstnon-magnetic metal electrode. A free magnetic metal layer may then bepresent on the first magnetic insulating tunnel barrier reference layer.A second magnetic insulating tunnel barrier reference layer is presenton the free magnetic metal layer, and a second non-magnetic metalelectrode is present on the second magnetic insulating tunnel barrier.In the memory device, the first and second magnetic insulating tunnelbarrier reference layers are arranged so that their magnetizations arealigned to be anti-parallel.

In yet another embodiment of the present disclosure, a spin torquetransfer magnetic random access memory device is provided that includespositioning a magnetic tunnel junction stack between a pair ofelectrodes, in which the MTJ stack includes at least one spin filters,e.g., a first and second magnetic insulating tunnel barrier referencelayer. In one embodiment, the magnetic tunnel junction stack comprisinga first magnetic insulating tunnel barrier reference layer that isdirect contact with a first face of a free magnetic metal layer and asecond magnetic insulating tunnel barrier reference layer that ispresent in direct contact with a second face of the free magnetic metallayer, wherein the first and second magnetic insulating tunnel barrierreference layers are arranged so that their magnetizations are alignedto be anti-parallel. In another embodiment, a first magnetic insulatingtunnel barrier reference layer that is direct contact with a first faceof a free magnetic metal layer, and a non-magnetic insulating tunnelbarrier is present on a second face of the free magnetic metal layer,and a magnetic metallic reference layer is present on the non-magneticinsulating tunnel barrier layer.

In another embodiment, a method of forming a memory device is providedthat includes forming a first magnetic insulating tunnel barrierreference layer on a first non-magnetic electrode that is present on asubstrate, wherein the magnetization of the first magnetic insulatingtunnel barrier reference layer is in a first direction. A free magneticmetal layer may then be formed on the first magnetic insulating tunnelbarrier reference layer. A second magnetic insulating tunnel barrierreference layer is formed on the free magnetic metal layer, wherein themagnetization of the second magnetic insulating tunnel barrier referencelayer is in a second direction, the first direction and the seconddirection being aligned to be antiparallel. A second non-magneticelectrode is then formed on the second magnetic insulating tunnelbarrier reference layer.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The disclosure will provide details in the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1 is a side cross-sectional view depicting one embodiment of a spintorque transfer magnetic random access memory device that includesforming a magnetic tunnel junction stack between a pair of electrodes,in which the magnetic tunnel junction stack includes a first and secondmagnetic insulating tunnel barrier reference layers on opposite sides ofa free magnetic metal layer that are arranged so that theirmagnetizations are aligned to be anti-parallel, in accordance with thepresent disclosure.

FIG. 2A is a plot illustrating the low switching current that resultsfrom the use of magnetic insulating tunnel barrier reference layers, inaccordance with present disclosure.

FIG. 2B is a plot illustrating the ratio of the single magnetic tunneljunction (MTJ) result to the double spin filter tunnel junction.

FIG. 3 is a side cross-sectional view depicting forming a firstnon-magnetic metal electrode on a substrate for an initial process stepin a method of forming a spin torque transfer magnetic random accessmemory device, in accordance with one embodiment of the presentdisclosure.

FIG. 4 is a side cross-sectional view depicting forming magnetic tunneljunction (MTJ) stack including a first magnetic insulating tunnelbarrier reference layer on a first side of a free magnetic metal layer,and a second magnetic insulating tunnel barrier reference layer on asecond side of the free magnetic metal layer, in accordance with oneembodiment of the present disclosure.

FIG. 5 is a side cross-sectional view depicting forming a secondnon-magnetic metal electrode on the MJT stack.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Detailed embodiments of the claimed structures and methods are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely illustrative of the claimed structures and methods that maybe embodied in various forms. In addition, each of the examples given inconnection with the various embodiments are intended to be illustrative,and not restrictive. Further, the figures are not necessarily to scale,some features may be exaggerated to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the methods and structures of the present disclosure. Forpurposes of the description hereinafter, the terms “upper”, “lower”,“right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, andderivatives thereof shall relate to the embodiments of the disclosure,as it is oriented in the drawing figures. The terms “positioned on”means that a first element, such as a first structure, is present on asecond element, such as a second structure, wherein interveningelements, such as an interface structure, e.g. interface layer, may bepresent between the first element and the second element. The term“direct contact” means that a first element, such as a first structure,and a second element, such as a second structure, are connected withoutany intermediary conducting, insulating or semiconductor layers at theinterface of the two elements.

As used herein, the term “memory device” means a structure in which theelectrical state can be altered and then retained in the altered state,in this way a bit of information can be stored. Spin torque transfermagnetic random access memory (STT MRAM) uses magnetic materials as thememory storage element. In some examples, STT MRAM uses memory storageelements that take advantage of the effect in which a current that ispassed through a magnetic material, such as a magnetic tunnel junction(MTJ)—reverses its direction of magnetization. Passing a current throughthe MTJ causes its direction of magnetization to switch between aparallel or anti-parallel state, which has the effect of switchingbetween low resistance and high resistance. Because this can be used torepresent the 1 s and 0 s of digital information, STT MRAM can be usedas a non-volatile memory. Reading STT MRAM involves applying a voltageto the MTJ to discover whether the MTJ offers high resistance to current(“1”) or low (“0”). Typically, a MTJ stack includes reference layer(s)(also referred to as pinned layer), tunnel layer(s) and free layer(s). Atypical MTJ stack is usually configured such either or both of thereference layer and tunnel barrier are disposed beneath the free layer.

It should be noted that exemplary materials for the free layer(s)include alloys and/or multilayers of Fe, Ni, Co, Cr, V, Mn, Pd, Pt, B, Oand/or N. Further, the reference layer(s) 108 can be composed of alloysand/or multilayers of Fe, Ni, Co, Cr, B, Mn, Pt, Pd, Ru, Ta, W and/orCu. Moreover, the tunnel barrier layer (s)can be composed of MgO, Al₂O₃,TiO₂, or materials of higher electrical tunnel conductance, such assemiconductors or low-bandgap insulators.

In some embodiments, a spin torque MRAM uses a 2 terminal device with apinned layer, tunnel barrier, and free layer in a magnetic tunneljunction stack. The magnetization of the pinned layer is fixed indirection (say pointing up) and a current passed down through thejunction makes the free layer parallel to the pinned layer, while acurrent passed up through the junction makes the free layeranti-parallel to the pinned layer. A smaller current (of eitherpolarity) is used to read the resistance of the device, which depends onthe relative orientations of the magnetizations of the free and pinnedlayers. The resistance is typically higher when the magnetizations areanti-parallel, and lower when they are parallel (though this can bereversed, depending on the material). It has been determined that one ofthe challenges in spin torque MRAM devices is to lower the switchingcurrent.

In some embodiments, the methods and structures of the presentdisclosure replace the tunnel barriers and pinned layers with magneticinsulating tunnel barrier reference layers. These layers are bothmagnetic and insulating, and are commonly referred to as spin filters.The term “magnetic” as used to describe the spin filter material layer,which is also referred to as a magnetic insulating tunnel barrierreference layer, may have a magnetization ranging from 50 emu/cm³ to 600emu/cm³. The term “insulating” as used to describe the spin filtermaterial layer, which is also referred to as a magnetic insulatingtunnel barrier reference layer, may denote a material having a roomtemperature resistance-area product of more than 0.1 Ohm-um².

In some embodiments, the methods and structures that are disclosedherein combine two of magnetic insulating tunnel barrier referencelayers with their magnetizations aligned anti-parallel, sandwiching amagnetic metallic free layer. In some embodiments, it can be arequirement of the device that all magnetizations are perpendicular tothe wafer. The higher spin polarization of the spin filters incomparison to prior devices using a combination of tunneling layer andpinned layers dramatically lowers the switching current. The methods andstructures of the present disclosure are now discussed with more detailreferring to FIGS. 1-5.

FIG. 1 depicts one embodiment of a spin torque transfer magnetic randomaccess memory device 100 that includes a magnetic tunnel junction (MTJ)stack 50 positioned between a pair of electrodes 5, 10, in which the MTJstack 50 includes spin filters, e.g., a first and second magneticinsulating tunnel barrier reference layer 15, 25. In some embodiments,the magnetic tunnel junction stack 50 includes a first magneticinsulating tunnel barrier reference layer 15 that is direct contact witha first face of a free magnetic metal layer 20 and a second magneticinsulating tunnel barrier reference layer 25 that is present in directcontact with a second face of the free magnetic metal layer 20. Thefirst and second magnetic insulating tunnel barrier reference layers 15,25 are arranged so that their magnetizations M1, M2 are aligned to beanti-parallel. The first and second magnetic tunneling barrier referencelayers 15, 25 replace the combination of separate magnetic metalreference layers and nonmagnetic insulating tunnel barrier layers inprior spin torque transfer magnetic random access memory devices, inwhich these combinations of separate magnetic metal reference layers andnonmagnetic insulating tunnel barrier layers are present on opposingsides of the free magnetic metal layer 20.

Referring to FIG. 1, the free magnetic metal layer 20 may be the layerin which the magnetization can be reversed forming the basis for writingbits in the spin torque transfer MRAM 100. The spin torque transfer MRAM100 is present on a substrate 2 that may be provided a semiconductormaterial, such as silicon (Si), insulating material, such as glass, or ametal material. The magnetization of the free magnetic metal layer 20may be switched by a spin torque induced from at least one of theneighboring first and second magnetic insulating tunnel barrierreference layers 15, 25.

In some embodiments, the free magnetic metal layer 20 may be a singleferromagnetic layer. For example, the free magnetic metal layer 20 maybe comprised of cobalt iron boride (CoFeB), but other materials may alsobe suitable for use as the free magnetic metal layer. In other examples,the free magnetic layer 20 may be composed of alloys and/or multilayersof Fe, Ni, Co, Cr, V, Mn, Pd, Pt, B, O and/or N. The thickness of thefree magnetic metal layer 20 may be less than 10 Å thick, and in someembodiments may range in thickness from 10 nm to 5 Å.

As described above, in prior STT MRAM devices two separate layers, i.e,an insulating tunnel layer and a magnetic reference layer (pinned layer)function together to provide a spin polarization via a tunnel magnetoresistance (TMR) effect. Tunnel magnetoresistance (TMR) is amagnetoresistive effect that occurs in a magnetic tunnel junction (MTJ),which is a component consisting of two ferromagnets separated by a thininsulator. When the insulating layer is thin enough (typically a fewnanometers), electrons can tunnel from one ferromagnet into the other.

In the present disclosure, each pairing of those layers is replaced witha magnetic insulating tunnel barrier reference layers that provides bothfunctions of the separate insulating tunnel layer and the magneticreference layer used in prior devices. In some embodiments, at least oneof the first and second magnetic insulating tunnel barrier referencelayers 15, 25 provide a spin torque effect that can cause switching inthe free magnetic metal layer 20, which can provide the basis forwriting bits in a the spin torque transfer MRAM 100 device. For example,electrons flowing through one of the first and second magneticinsulating tunnel barrier reference layers 15, 25 acquire a spinpolarization from the first and second magnetic insulating tunnelbarrier reference layers 15, 25 that the electrons are travelingthrough, which then can exert a spin torque on the free magnetic metallayer 20, which can switch the magnetic direction of the free magneticmetal layer. For example, in some embodiments, at current densities onthe order of approximately 10⁶ to 10⁷ A/cm², the spin torque produced bythe first and second magnetic insulating reference layers 15, 25 cancause the free magnetic metal layer 20 to switch, i.e., reverse itsmagnetization direction.

In some embodiments, the first and second magnetic insulating tunnelbarrier reference layers 15, 25 may be composed of cobalt iron oxide(CoFeO_(x)). In other embodiments, the first and second magneticinsulating tunnel barrier reference layers 15, 25 may be composed of anallow of cobalt (Co), iron (Fe), and oxygen (O), as well as at least oneother element, such as CoFeAOx, wherein A may be any element selectedfrom the group consisting of beryllium (Be), boron (B), magnesium (Mg),aluminum (Al), silicon (Si), calcium (Ca), scandium (Sc), titanium (ti),vanadium (V), chromium (Cr), zinc (Zn), a 4d transition metal, a 5dtransition metal, and a combination thereof. Examples of 4d transitionmetals that are suitable for providing A in CoFeA include yttria (Y),zirconia (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium(Ru), rhenium (Rh), palladium (Pd), silver (Ag), cadmium (Cd) andcombinations thereof. Examples of 5d transition metals that are suitablefor providing A in CoFeA include lutetium (Lu), hafnium (Hf), tantalum(Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum(Pt), gold (Au) and mercury (Hg).

It is noted that the above examples are provided for illustrativepurposes only and are not intended to limit the present disclosure.Other examples of materials suitable for providing the first and secondmagnetic insulating tunnel barrier reference layers 15, 25 include(La_(1-x)Sr_(x))MnO₃ and related materials in which La is replaced withother rare earth metals and Sr is replaced by Pb, Ca and Ba. Forexample, (La_(0.9)Sr_(0.1))MnO₃ or (La_(0.9)Ca_(0.1))MnO₃ can be used,where x=0.1 for both Sr and Ca. In other embodiments, insulatingferrimagnets may provide the first and second magnetic insulating tunnelbarrier reference layers 15, 25 and can be selected from materialshaving the crystal structure of spinels or garnets. Suitable spinelsinclude materials such as CoFe₂O₄, Li_(0.5)Fe_(2.5)O₄,Mn_(0.5)Zn_(0.5)Fe₂O₄. Suitable garnets include materials such asY₃Fe₅O₁₂, Y₃Fe_((5-2x))Co_(x)Ge_(x)O₁₂.

In some embodiments, each of the first and second magnetic insulatingtunnel barrier reference layers 15, 25 may be composed of aferromagnetic material having a high magnetic polarization value (P)and, accordingly it may be formed of materials that have magneticpolarization values that are high (P>50%) and ultra-high (P^(˜)90%). Itis noted that each of the first and second magnetic insulating tunnelbarrier reference layers 15, 25 may have a thickness of 100 Å or less.In some embodiments, the thickness of each of the first and secondmagnetic insulating tunnel barrier reference layers 15, 25 may range inthickness from 10 nm to 5 Å. It is noted that in some embodiments, thefirst magnetic insulating tunnel barrier reference layer 15 may bepresent directly on a first face of the free magnetic metal layer 20,and the second magnetic insulating tunnel barrier reference number 25may be present directly on an opposing second face of the free magneticmetal layer 20. In this manner, there is no interfacial material betweeneither of the first and second magnetic insulating tunnel barrierreference layers 15 and the free magnetic metal layer.

It is noted that the magnetization M1, M2 for both of the first andsecond magnetic insulating tunnel barrier reference layers 15, 25 is ina direction that is perpendicular to the surface of the substrate 2 thatthe spin torque transfer magnetic random access memory device 100 ispresent on. By being perpendicular to the upper surface of the substratethat the spin torque transfer magnetic random access memory device 100is present on, it is meant that the direction of magnetization M1, M2for both the first and second magnetic insulating tunnel barrierreference layer 15, 25 is “anti-parallel”.

A first electrode 5 may be present in contact with the first magneticinsulating tunnel barrier reference layer 15, and a second electrode 10may be in contact with the second magnetic insulating tunnel barrierreference layer 25. In some examples, the first and second electrodes 5,10 are non-magnetic. By “non-magnetic” it is meant that the material ofthe first and second non-magnetic electrode is not strongly affected bya magnetic field and is unable to magnetized. Examples of metals thatare suitable for the first and second electrode 5, 10 may include copper(Cu), aluminum (Al), platinum (Pt), gold (Au), silver (Ag), tantalum(Ta), titanium (Ti), ruthenium (Ru), and tungsten (W). It is noted thateach of the first and second magnetic insulating tunnel barrierreference layers 15, 25 may have a thickness of 100A or less. In someembodiments, the thickness of each of the first and second magneticinsulating tunnel barrier reference layers 15, 25 may range in thicknessfrom 100 nm to 5 Å.

In some embodiments, the first non-magnetic electrode 5 is in directcontact with the first magnetic insulating tunnel barrier referencelayer 15, which is in direct contact with a first side of a freemagnetic metal layer 20, e.g., a free magnetic metal layer provided by asingle material layer. This arrangement means that there is only asingle material layer of the first magnetic insulating tunnel barrierreference layer 15 is between the free magnetic metal layer 20 and thefirst non-magnetic electrode 5. In some embodiments, the secondnon-magnetic electrode 10 is in direct contact with the second magneticinsulating tunnel barrier reference layer 25, which is in direct contactwith a first side of a free magnetic metal layer 20, e.g., a freemagnetic metal layer provided by a single material layer. Thisarrangement means that there is only a single material layer of thesecond magnetic insulating tunnel barrier reference layer 25 is betweenthe free magnetic metal layer 20 and the second non-magnetic electrode10.

In accordance with some embodiments of the present disclosure, the spintorque MRAM 100 of the present disclosure replaces the tunnel barriersand pinned layers by magnetic insulating tunnel barrier reference layers15, 25, in which these layers are both magnetic and insulating, and arecommonly referred to as spin filters. As depicted in FIG. 1, the firstand second magnetic insulating tunnel barrier reference layers 15, 25have their magnetizations aligned antiparallel, sandwiching the magneticmetallic free layer 20. In some embodiments, all magnetizationdirections, i.e., the magnetization directions for the first and secondmagnetic insulating tunnel barrier reference layers 15, 25 and the freemagnetic layer 20, are perpendicular to the substrate 2. The higher spinpolarization of the spin filters, i.e., first and second magneticinsulating tunnel barrier reference layers 15, 25 dramatically lowersthe switching current of the spin torque MRAM 100.

FIGS. 2A and 2B illustrate the low switching current that results fromthe use of magnetic insulating tunnel barrier reference layers 15, 25,in accordance with present disclosure. FIGS. 2A and 2B illustrate plotsfrom a single domain model in which the plots include calculations forboth the double spin filter tunnel junction and a single junction. Forthe single junction, there are two different switching currents, one forswitching from 0 to 1 and one for switching from 1 to 0. Since thetransistor must be sized for the larger of the two, only the switchingcurrent for 0 to 1 is depicted in FIG. 2A. The ratio of the single MTJresult to the double spin filter tunnel junction is shown in FIG. 2B.P_(T), P_(B), P_(F), and P_(F′) are the spin polarizations of the topreference layer, bottom reference layer, top interface of the freelayer, and bottom interface of the free layer. α is the magnetic dampingand Eb is the activation energy. As P_(T), P_(B), P_(F), and P_(F′) allgo to 1, the switching currents decrease more rapidly for the doublejunction. The examples use activation energy Eb=60 kT and magneticdamping α=0.004.

In another aspect of the present disclosure, a method of forming amemory device 100 is provided that includes forming a first magneticinsulating tunnel barrier reference layer 15 on a first non-magneticelectrode 5, wherein the magnetization of the first magnetic insulatingtunnel barrier reference layer 5 is in a first direction M1. A freemagnetic metal layer 20 may then be formed on the first magneticinsulating tunnel barrier reference layer 25. A second magneticinsulating tunnel barrier reference layer 25 is formed on the freemagnetic metal layer 20, wherein the magnetization of the secondmagnetic insulating tunnel barrier reference layer 25 is in a seconddirection M2. Each of the first and second directions are anti-parallel.A second non-magnetic electrode 10 is then formed on the second magneticinsulating tunnel barrier reference layer 25. The details of oneembodiment of aforementioned embodiment are now described with referenceto FIGS. 3-5.

Referring to FIG. 3, a first non-magnetic metal electrode 5 is formed ona substrate 2. The first non-magnetic metal electrode 5 may be ametallic layer or may be an electrically conductive element of CMOS(complementary metal-oxide-semiconductor) circuitry or directly a drainor a source of select transistor(s) which are controlled by a wordline(s). The first non-magnetic metal electrode 5 may be blanketdeposited atop the substrate 2. For example, the first non-magneticmetal electrode 5 may be blanket deposited using a physical vapordeposition (PVD) process. Examples of physical vapor depositionprocesses suitable for forming the first non-magnetic metal electrode 5include plating, electroplating, and sputtering. In other embodiments,the first non-magnetic metal electrode 5 may be formed using chemicalvapor deposition.

Referring to FIG. 4, the MTJ stack 50 can be blanket formed on the firstnon-magnetic metal electrode 5. In some embodiments, forming the MTJstack 50 may begin with directly depositing the first magneticinsulating tunnel barrier reference layer 15 on a first non-magneticelectrode 5. The first magnetic insulating tunnel barrier referencelayer 15 may be deposited directly on the first non-magnetic electrode 5using a physical vapor deposition (PVD) process. Examples of physicalvapor deposition processes suitable for forming the first non-magneticmetal electrode include plating, electroplating, and sputtering. Inother embodiments, the first non-magnetic metal electrode 5 may beformed using physical vapor deposition or chemical vapor deposition. Forexample, the first non-magnetic metal electrode 5 may be formed using amethod that may include plating, electroplating, electroless plating andsputtering. The magnetization of the first magnetic insulating tunnelbarrier reference layer 5 is in a first direction M1 that isanti-parallel.

In a following process step, the free magnetic metal layer 20 is formedon the first magnetic insulating tunnel barrier reference layer 15. Insome embodiments, the free magnetic layer 20 may be deposited directlyon the first magnetic insulating tunnel barrier reference layer 15. Thefree magnetic layer 20 may also be formed using a deposition process,such as chemical vapor deposition, physical vapor deposition, plating,electroplating, electroless plating, sputtering and a combinationthereof. The free magnetic layer 20 may also be formed having adirection of magnetization that is anti-parallel to the upper surface ofthe substrate 2. The magnitude of direction in the free magnetic metallayer 20 may be switched in response to a spin torque applied through atleast one of the first and second magnetic insulating tunnel barrierreference layer 15, 25.

Still referring to FIG. 4, the second magnetic insulating tunnel barrierreference layer 25 may then be formed on the free magnetic metal layer20. The second magnetic insulating tunnel barrier reference layer 25 canbe deposited directly on the free magnetic metal layer 20 using methodssimilar to the methods described above for forming the first magneticinsulating tunnel barrier layer 15. Therefore, the description of theforming methods for forming the first magnetic insulating tunnel barrierreference layer 25 may be suitable for describing the second magneticinsulating tunnel barrier reference layer 15.

Referring to FIG. 5, the method can continue with forming a secondnon-magnetic metal electrode 10 on the upper surface of the MJT stack50. The second non-magnetic metal electrode 10 may be deposited directlyon the second magnetic insulating tunnel barrier reference layer 25. Thesecond non-magnetic metal electrode 10 may be formed using physicalvapor deposition or chemical vapor deposition methods similar to thosedescribed above for forming the first magnetic metal electrode 5, asdescribed above with reference to FIG. 3. Therefore, the description ofthe deposition methods, such as chemical vapor deposition and physicalvapor deposition, that have been described above in FIG. 3 for formingthe first non-magnetic metal electrode 5 is suitable for forming thesecond non-magnetic metal electrode 10.

The material stack depicted in FIG. 5 may then be patterned and etchedto provide the spin torque transfer magnetic random access memory device100 that is depicted in FIG. 1. For example, the material stack depictedin FIG. 5 may be patterned and etched using deposition, photolithographyand a selective etching process. Specifically, a pattern is produced byapplying a photoresist to the surface to be etched; exposing thephotoresist to a pattern of radiation; and then developing the patterninto the photoresist utilizing a resist developer. Once the patterningof the photoresist is completed, the sections covered by the photoresistare protected while the exposed regions are removed using a selectiveetching process that removes the unprotected regions. The photoresistpattern is then transferred into the material stack using an etchprocess. The etch process may be an anisotropic etch. As used herein, an“anisotropic etch process” denotes a material removal process in whichthe etch rate in the direction normal to the surface to be etched isgreater than in the direction parallel to the surface to be etched. Theanisotropic etch may include reactive-ion etching (RIE). Other examplesof anisotropic etching that can be used at this point of the presentinvention include ion beam etching, plasma etching or laser ablation.Next the photoresist pattern is removed by a wet or dry etch to providethe structure depicted in FIG. 1.

The methods and structures that have been described above with referenceto FIGS. 1-5 may be employed in any electrical device. For example, thememory devices that are disclosed herein may be present withinelectrical devices that employ semiconductors that are present withinintegrated circuit chips. The integrated circuit chips including thedisclosed interconnects may be integrated with other chips, discretecircuit elements, and/or other signal processing devices as part ofeither (a) an intermediate product, such as a motherboard, or (b) an endproduct. The end product can be any product that includes integratedcircuit chips, including computer products or devices having a display,a keyboard or other input device, and a central processor.

It should be further understood that STT MRAM devices according to thepresent principles can be employed in any computing apparatus thatutilizes RAM. For example, such computing apparatuses can utilize theSTT MRAM devices in lieu of or in addition to RAM. Such computingapparatuses can include personal computers, mainframes, laptops, smartphones, tablet computers and other computing devices.

Having described preferred embodiments of STT MRAM devices, apparatusesand manufacturing methods (which are intended to be illustrative and notlimiting), it is noted that modifications and variations can be made bypersons skilled in the art in light of the above teachings. It istherefore to be understood that changes may be made in the particularembodiments disclosed which are within the scope of the invention asoutlined by the appended claims. Having thus described aspects of theinvention, with the details and particularity required by the patentlaws, what is claimed and desired protected by Letters Patent is setforth in the appended claims.

What is claimed is:
 1. A method of forming a memory device comprising:forming a first magnetic insulating tunnel barrier reference layer on afirst metallic electrode that is present on a substrate, wherein themagnetization of the first magnetic insulating tunnel barrier referencelayer is in a first direction; forming a free magnetic metal layer onthe first magnetic insulating tunnel barrier reference layer; forming asecond magnetic insulating tunnel barrier reference layer on the freemagnetic metal layer, wherein the magnetization of the second magneticinsulating tunnel barrier reference layer is in a second direction, thefirst direction and the second direction being aligned to beantiparallel to an upper surface of the substrate; and forming a secondmetallic electrode on the second magnetic insulating tunnel barrierreference layer.
 2. The method of claim 1, wherein the first magneticinsulating tunnel barrier reference layer and comprises cobalt ironoxide (CoFeOx).
 3. The method of claim 1, wherein the second magneticinsulating tunnel barrier reference layer comprises cobalt iron oxide(CoFeOx).
 4. The method of claim 1, wherein the first magneticinsulating tunnel barrier reference layer comprises CoFeAO_(x), whereinA may be any element selected from the group consisting of beryllium(Be), boron (B), magnesium (Mg), aluminum (Al), silicon (Si), calcium(Ca), scandium (Sc), titanium (ti), vanadium (V), chromium (Cr), zinc(Zn), yttria (Y), zirconia (Zr), niobium (Nb), molybdenum (Mo),technetium (Tc), ruthenium (Ru), rhenium (Rh), palladium (Pd), silver(Ag), cadmium (Cd), lutetium (Lu), hafnium (Hf), tantalum (Ta), tungsten(W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au)mercury (Hg), and combinations thereof.
 5. The method of claim 1,wherein the second magnetic insulating tunnel barrier reference layercomprises CoFeAOx, wherein A may be any element selected from the groupconsisting of beryllium (Be), boron (B), magnesium (Mg), aluminum (Al),silicon (Si), calcium (Ca), scandium (Sc), titanium (ti), vanadium (V),chromium (Cr), zinc (Zn), yttria (Y), zirconia (Zr), niobium (Nb),molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhenium (Rh),palladium (Pd), silver (Ag), cadmium (Cd), lutetium (Lu), hafnium (Hf),tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir),platinum (Pt), gold (Au) mercury (Hg), and combinations thereof.
 6. Themethod of claim 1, wherein the free magnetic metal layer comprisesCoFeB.
 7. The method of claim 1, wherein the free magnetic metal layercomprises alloys and/or multilayers including elements selected from thegroup consisting of Fe, Ni, Co, Cr, V, Mn, Pd, Pt, B, O, N andcombinations thereof.
 8. The method of claim 1, wherein at least one ofthe first magnetic insulating tunnel barrier reference layer, the secondmagnetic insulating tunnel barrier reference layer and the free magneticmetal layer is deposited using physical vapor deposition.
 9. The methodof claim 1, wherein the memory device is a spin torque transfer magneticrandom access memory device.
 10. A method of forming a memory devicecomprising: forming a first magnetic insulating tunnel barrier referencelayer comprising cobalt and iron on a first metallic electrode that ispresent on a substrate, wherein the magnetization of the first magneticinsulating tunnel barrier reference layer is in a first direction;forming a free magnetic metal layer on the first magnetic insulatingtunnel barrier reference layer; forming a second magnetic insulatingtunnel barrier reference layer comprising cobalt and iron on the freemagnetic metal layer, wherein the magnetization of the second magneticinsulating tunnel barrier reference layer is in a second direction, thefirst direction and the second direction being aligned to beantiparallel to an upper surface of the substrate; and forming a secondmetallic electrode on the second magnetic insulating tunnel barrierreference layer.
 11. The method of claim 10, wherein the first magneticinsulating tunnel barrier reference layer and comprises cobalt ironoxide (CoFeOx).
 12. The method of claim 10, wherein the second magneticinsulating tunnel barrier reference layer comprises cobalt iron oxide(CoFeOx).
 13. The method of claim 10, wherein the first magneticinsulating tunnel barrier reference layer comprises CoFeAOx, wherein Amay be any element selected from the group consisting of beryllium (Be),boron (B), magnesium (Mg), aluminum (Al), silicon (Si), calcium (Ca),scandium (Sc), titanium (ti), vanadium (V), chromium (Cr), zinc (Zn),yttria (Y), zirconia (Zr), niobium (Nb), molybdenum (Mo), technetium(Tc), ruthenium (Ru), rhenium (Rh), palladium (Pd), silver (Ag), cadmium(Cd), lutetium (Lu), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium(Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au) mercury (Hg),and combinations thereof.
 14. The method of claim 10, wherein the secondmagnetic insulating tunnel barrier reference layer comprises CoFeAOx,wherein A may be any element selected from the group consisting ofberyllium (Be), boron (B), magnesium (Mg), aluminum (Al), silicon (Si),calcium (Ca), scandium (Sc), titanium (ti), vanadium (V), chromium (Cr),zinc (Zn), yttria (Y), zirconia (Zr), niobium (Nb), molybdenum (Mo),technetium (Tc), ruthenium (Ru), rhenium (Rh), palladium (Pd), silver(Ag), cadmium (Cd), lutetium (Lu), hafnium (Hf), tantalum (Ta), tungsten(W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au)mercury (Hg), and combinations thereof.
 15. A method of claim 10,wherein the free magnetic metal layer comprises CoFeB.
 16. The method ofclaim 10, wherein the free magnetic metal layer comprises alloys and/ormultilayers including elements selected from the group consisting of Fe,Ni, Co, Cr, V, Mn, Pd, Pt, B, O, N and combinations thereof.
 17. Themethod of claim 10, wherein at least one of the first magneticinsulating tunnel barrier reference layer, the second magneticinsulating tunnel barrier reference layer and the free magnetic metallayer is deposited using physical vapor deposition.
 18. The method ofclaim 10, wherein the memory device is a spin torque transfer magneticrandom access memory device.